Loss of secondary means of escape

[jokar]

Ashley,

4 hours in and a 30 minute break, ok for workers perhaps but not for shoppers.  Those with health problems may not be allowed to enter such a system.

[wee brian]

Jokar
I assume that Oxy reduct needs a reasonably leek free enclosure to work.

Kurnal - I see your point.

Ian G - agreeing with me Ian - whatever next.

[Ashley Wood]

Ashley the heads are in the wrong place!!!

There is no point spraying mist into smoke that has come from a fire in and adjacent room. All you will get is wet.

Remember that an added bonus with High pressure water mist systems is the 'smoke washing' capability. This is briefly what happens, the large smoke particulate is absorbed by the finer water mist droplet and this makes the droplet heavy. It then drops to the floor and on a large scale, creates a survivable condition within the area that is becoming smoke logged. It also reduces temperature within the stairwell dramatically. The only down side with the actual project is that the smoke washing effect only comes into effect when the heat has activated the glass bulb, hence my earlier comment about open nozzles being best.

I agree that total coverage within rooms and escape routes would be the very best scenario.

[wee brian]

Ashley

Ive heard tell of this "smoke scrubbing" effect before. Sprinklers are supposed to do it as well. (with droplets larger than the smoke particles).

I am not sure there is any evidence of the mechanism you describe just that there appears to be a reduction in some of the nasties that have been measured in experiments. I am not sure there are any data available for fires occuring outside the protected area.

If there is any info on this I'd be interested to see it.

As you say the thermal actuation of the mist system would be serious draw back if you were relying on it to "scrub" smoke entering the stair enclosure from adjacent accomodation. Open heads and AFD operation is better but liable to unwanted activations.

[Ashley Wood]

Wee Brian,

I believe you may be right regarding test data availability for smoke scrubbing in an area outside the fire effected area. I will look into this. You mention sprinklers having an ability to do the same as water mist. This is true but the droplet size compared to a high pressure mist (HPWM) droplet is huge i.e 1000 micron compared to 60-100 micron for HPWM. What this means is that the free fall velocity of the sprinkler droplet is greater than that of the HPWM. In other words the HPWM floats in the air absorbing 'sooty' particles until it gets to heavy.

It is true to say that none of these systems are able to reduce smoke in its entirety, it tends to be only the visible particulate, nonetheless, very impressive when you see it work and breath the results without  BA.

[kurnal]

And in addition to the slower free fall velocity the surface area of water is infinitely larger, so therefore should be much more effective. But how much is the question. I have seen manufacturers claims and some test data but I have never seen any independent  accredited test results.

[Ashley Wood]

There were some tests done by a guy called 'Jack Mawiney' of Hughes associates in the USA. I am trying to get more information.